Lovato, 25, tweeted: "I write this through tears of frustration and sadness that I have to postpone my concert in London at the O2 tonight due to being very, very sick and with swollen vocal chords that were examined by an ENT (dr.).

"If I go on tonight and injure my vocal chords any more I could potentially have to cancel the rest of my tour.

"I'm so so so sorry to disappoint any of my fans in London that have traveled hours to be here by plane or car, and to all of the fans that got these tickets for their birthday, holiday or any other special occasion.

"It breaks my heart to let you down. Juts know I feel your frustration and I wouldn't do his unless I absolutely had to.